Process for the gaseous cementation of steel pieces



arch 25, 1941.2 s s 2,235,947

PROCESS FOR THE GASEOUS GEMENTAI'ION OF STEEL PIECES Filed March 13, 1-939 In vie 77%,;

Patented Mar. 25, 1941 PATENT OFFICE PROCESS FOR THE GASEOUS CEMENTATION OF STEEL PIECES Leon Salves, Billancourt,

France, assignor to Louis Renault, Billancourt, France Application March 13, 1939, Serial No.

In France March 30, 1938 1 Claim.

The modern methods for gaseous cementation by carbon may give uniform and constant results when these are applied to furnaces in which the pieces are subject to movement, such as fura naces with rotating retort for small pieces, continuous furnaces oi the propelling type, furnaces with revolving hearth, and the like, but the results are irregular in the case oi cementation. in. stationary muilies of large size. In fact, the

in gas inlets and outlets are also in the fixed position, and the composition of the gaseous atmosphere will gradually vary throughout the entire path of the gas, from the inlet to the discharge. The pieces which are situated outside this path it will be subjected to a calm atmosphere having slight whirls, and in such places the cementation is imperfect, owing to the exhaustion of the gas.

The same is true for the cementation of small pieces contained in baskets, or for the cementapn tion in the cavities of the pieces; in this case the gas is imperfectly renewed by difiusion, it becomes exhausted, and the cementation will not continue.

in the case of gaseous cementation by ampm monia. at about 520 0., such drawbacks have been obviated by stirring up the atmosphere by a tan which is located in the mufiie and is driven by a shaft passing through the same, but for cementation by carbon, this method cannot be an employed, owing to the very high temperature, which is between 800 and 1000 according to the case (usually about 930).

The present invention consists in obtaining, by a static method and without any heated mechpp anism, the homogeneous nature of the gaseous composition throughout the whole of the cementation mume.

For this purpose, I produce sudden periodic variations of pressure having a great value. For

it instance, by any suitable method which can be readily conceived, I suddenly send into the cementation muflle a volume of gas comparable with the volume of the muiiie. This will cause a sudden increase of pressure, but owing to the gas discharge conduit and to the inevitable leakage at the charging door (even though this is as tight as possible), the pressure will gradually fall to a value near atmospheric pressure. At this time,

50 i. e., in a few minutes, another sudden supply of gas will increase the pressure.

The frequency of this pulsatory action is sufficiently low in order that at each instant the equilibrium of pressure shall be practically atg; tained at all points of the muffle. The admission 01' gas is sufficiently abrupt in order that the rise or pressure shall be as great as desired.

The volume of gas supplied at each pulsation, the time between any two pulsations, and the rapidity of the injection, are regulated according to the volume of the mume, the leakage at the charging door (or at the evacuation conduit), and the supply of gas required for a uniform and homogeneous cementation.

For operating the process, the subject-matter of the invention, use may be made of various devices adapted to provide a. periodic supply of a large quantity of gas.

As examples which are not of a iimitative nature, the following description relates to two such devices, with reference to the two figures of the accompanying drawing, in which Fig. i is a diagrammatic view of one form of device for practicing the process of the invention, certain of the parts being shown in full lines and certain other parts shown in section, and

Fig. 2 is a similar view of another form of device for practicing the invention.

The device which is shown diagrammatically in Fig. 1 comprises a supercompressor I which receives-through the pipe 2--the gas supplied by the preparatory apparatus and delivers this gas into a recipient 3, whose periodic discharge into the cementation muiiie 4 is assured by a gatevalve 5 which is controlled by the maximum pressure prevailing in the recipient 3, or by a clockwork device. At each discharge, the pressure rises rapidly in the interior of the muflie, and then falls more slowly until the next discharge, owing to the exit of the exhausted gas through the evacuation conduit 6 or to leakage which may occur in spite of the tight door I.

In the device shown diagrammatically in Fig. 2, the recipient 3 is replaced by a compressible rubher bag 8 which is supplied through a gate-valve 9 and discharges through a gate-valve In. The m discharge from the bag may be obtained by compressing the said bag by means of a fluid (compressed air or water under pressure) which is sent around the bag into a recipient containing this latter. The said fluid is delivered into the recipient through a gate-valve l2, and. it is discharged through a gate-valve I3. The valves 9 and III on the one hand, and i2 and I3 on the other hand, are automatically controlleid insuch 50 manner (for instance) that the valves 9 and I3 will be opened and the valves in and 12 will be closed during the filling of the bag, and that the valves 9 and I3 will be closed and the valves l0 and I2 opened during the emptying of the bag. I:

The valves 9, I0 and l2, l3 may be controlled by electric means or by clockwork; and they may be combined together or assembled in a single apparatus.

I claim:

In a process for the cementation of steel articles in a stationary muflle, the step which consists in periodically supplying fresh cementatlon gas under high pressure intermittently to the mume, whereby the pressure in the muille will rise abruptly and will then gradually tall to its initial value whereby fresh cementatlon gas comes in contact with all parts of the surtace 0i 5 the steel articles.

LEON SAIVES. 

